1. Field of the Invention
The present invention relates to a digital television receiver and an antenna control method in a digital television receiver.
2. Background of the Related Art
Researches for an antenna of a vestigial side band (VSB) modulation receiver selected as the standard of transmission type of a terrestrial channel for digital television broadcasting are still in their early stages and incomplete, but recently, the concepts and ideas thereof have been gradually proposed. Also, it is known that their standardization is now preparing in ATSC.
However, at present, any case of an antenna applied to a digital television receiver has not yet been open to the public and has not yet been commercialized.
The conventional antenna that can be used in the digital television receiver is briefly classified into two types.
One is an outdoor antenna. This outdoor antenna has a good receiving performance, but is large-sized and causes inconvenience in installation.
The other is an indoor antenna. This indoor antenna is small-sized and can be easily installed. However, it has a disadvantage that when the receiving sensitivity is lowered during viewing of a television broadcast, a user should manually adjust the directivity of the antenna as he/she is monitoring a displayed picture.
Meanwhile, in the terrestrial channel of the digital television broadcasting, many multi-paths and radio wave obstacles may exist. Thus, the receiving characteristic of the antenna of the digital television receiver may greatly affect the characteristic of the digital television receiver.
Hereinafter, problems of antennas according to their kinds and channel environments will be explained with reference to FIGS. 1 to 3.
FIG. 1 is a diagram illustrating an omni-directional antenna, FIG. 2 is a diagram illustrating a directional antenna, and FIG. 3 is a diagram illustrating a smart antenna.
First, the digital television receiver using the omni-directional antenna of FIG. 1 can receive a main signal in all directions only in channels wherein the main signal is strong and multi-path signals are weak. On the contrary, in the channels wherein the main signal is weak and the multi-path signals are strong such as downtown building areas or indoor antennas, it is not easy for the omni-directional antenna to receive a desired channel, and this deteriorates the performance of the digital television receiver.
Second, in order to solve the problem of the omni-directional antenna, the use of the directional antenna of FIG. 3 may be considered. However, under the environment where the channel state is continuously changed, the main signal may be intercepted by moving radio wave obstacles. In this case, it is not easy to receive the main signal in other directions, and this also deteriorates the performance of the digital television receiver. As described above, the omni-directional antenna and the directional antenna are in a mutual trade-off relation.
Third, in order to solve the problems of the omni-directional antenna and the directional antenna, the use of the smart antenna of FIG. 3 may be considered. The adoption of the smart antenna can solve the above-described problems, but the smart antenna should accompany an antenna control section that can effectively control the pattern and directivity of the smart antenna.
The smart antenna that can be applied to the digital television antenna may be classified into a phase array type, motor drive type, switching type, etc.
According to the phase array type and motor drive type, antenna patterns of the antenna are continuously provided. According to the switching type, N antenna patterns are switched as needed, and the signal is interrupted during the switching operation. This may exert a bad effect on various feedback loops in the digital television receiver.
In the terrestrial channels of the digital television broadcasting, a large number of multi-paths and radio wave obstacles exist. In case that the radio wave obstacle is static, the state of the antenna (i.e., beam width, direction, gain, pattern, etc. of the antenna) can be determined by monitoring the channel environment only once using the smart antenna.
In case that the radio wave obstacle is dynamic, the channel environment is also changed dynamically in process of time, and thus the state of the antenna should be also changed in conformity to the change of the channel environment.
However, while the antenna switching is performed, the digital television receiver cannot receive the signal. While the signal is not received, various feedback loops such as an automatic gain control loop, various kinds of sync signal recovery loop, symbol sync recovery loop, carrier recovery loop, equalizer, etc. constructed in the digital television receiver unconverge, or lock loops are unlocked. Consequently, the digital television receiver should converge or be initialized.
Such an abnormal state of the digital television receiver causes the displayed picture to be broken or frozen until the digital television receiver is in a normal state again, giving the user inconvenience.